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    Dealing with high amperages

    I'm working on an apartment complex that is getting a little uncomfortably-high in the amperage. Anyone want to shed some light on this topic?

    This multi-building, 75 unit apartment complex, 208 single phase service is showing roughly 3400A demand after nec factors and all have been applied. Eaton has gear that can handle up to 5000A for group metering but im hesitant to continue with design on one single service feed due to potential SCCR problems down the road.. I'm expecting my MDP and disconnect to be rated for 4000A... Is it pretty common to work with amperages these high in 208-1Ø? Any other possible concerns or problems i should be aware of down the road?

    #2
    My solution was to split the apartments and house into TWO separate services, both grouped in the same room.
    House board has a CT section for single meter.
    Apartment service has single main and branches serving the meter stacks on each floor. Designed where NO CBers could be added in this distribution equipment.
    120/208V-1P-3W to each apartment panel.

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      #3
      That's not a bad idea. So technically could i use this method of having a split system but still utilize (1) utility transformer. I've heard of it being done in the past just never personally had experience with it. Essentially show two separate feeders tapped off the one xfmr routed to my (2) 2000A distribution boards?

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        #4
        Originally posted by WA_Sparky View Post
        That's not a bad idea. So technically could i use this method of having a split system but still utilize (1) utility transformer. I've heard of it being done in the past just never personally had experience with it. Essentially show two separate feeders tapped off the one xfmr routed to my (2) 2000A distribution boards?
        Would that change any demand factors applied to the loads?

        You might wind up with 2 distribution boards each rated more than 2000A.

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          #5
          Originally posted by WA_Sparky View Post
          Essentially show two separate [COLOR=#FF0000]feeders [/COLOR]tapped off the one xfmr routed to my (2) 2000A distribution boards?
          Two separate services, big difference. And whether you have one or two utility transformers is really up to the PoCo, it might be easier all around for there to be more than one.

          How many physical buildings are involved? It could make sense to make each one a separate service; don't know how the PoCo would feel about that, though, you'd have to ask.

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            #6
            4000 amps 1Ø is not common around here. My current apartment complex project is 4-40000 amp 208Y/120 volt services 3Ø. Why wouldn't you use 3Ø?
            Rob

            Moderator

            All responses based on the 2017 NEC unless otherwise noted

            Comment


              #7
              Originally posted by infinity View Post
              4000 amps 1Ø is not common around here. My current apartment complex project is 4-[COLOR=#FF0000]40000[/COLOR] amp 208Y/120 volt services 3Ø. Why wouldn't you use 3Ø?
              Your tenants must have like six tesla chargers and a few hot-tubs per apartment....kidding
              I thought we were discussing 3P.
              The house board ranged from 1200-1600A depending on number apts/bldg. size and number of elevators.
              The apt board is where you get all your 220.84 discounts.

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                #8
                Originally posted by infinity View Post
                4000 amps 1Ø is not common around here. My current apartment complex project is 4-40000 amp 208Y/120 volt services 3Ø. Why wouldn't you use 3Ø?

                Yeah I was going to say the same thing. Not really sure if the OP meant actual single phase service or three phase service with single phase supply to each unit. I assume the latter but sounded more like the former was described. POCO's usually have a relatively low max demand they will supply to a single phase service.
                Ethan Brush - East West Electric. NY, WA. MA

                "You can't generalize"

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                  #9
                  Originally posted by infinity View Post
                  4000 amps 1Ø is not common around here. My current apartment complex project is 4-40000 amp 208Y/120 volt services 3Ø. Why wouldn't you use 3Ø?
                  Forty thousand amps?

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                    #10
                    4,000amps is typical for commercial, but always 3 phase over 400 amps.

                    Comment


                      #11
                      Originally posted by ggunn View Post

                      Forty thousand amps?
                      Obviously a typo (sorry about that),
                      here I fixed it:

                      Originally posted by infinity View Post
                      4000 amps 1Ø is not common around here. My current apartment complex project is 4-4000.0 amp 208Y/120 volt services 3Ø. Why wouldn't you use 3Ø?
                      Rob

                      Moderator

                      All responses based on the 2017 NEC unless otherwise noted

                      Comment


                        #12
                        My experience mirrors what has been stated. Start with POCO and see what options are available. Keep 230.2(C) in mind. Two service points might prove to be a cost advantage.
                        At my age, I'm accustomed to restaurants asking me to pay in advance, but now my bank has started sending me their calendar one month at a time.

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                          #13
                          Originally posted by infinity View Post

                          Obviously a typo (sorry about that),
                          here I fixed it:
                          What's a factor of ten between friends?

                          Comment


                            #14
                            Originally posted by oldsparky52 View Post

                            Would that change any demand factors applied to the loads?

                            You might wind up with 2 distribution boards each rated more than 2000A.
                            Yeah my demand will change for sure. Demand factor from 0.24 to 0.35 (if i went with 3 services at 25 units each. 1 per building). 220.84

                            Total of three buildings. They anticipate on adding another (3) buildings later on that are carbon copies of these buildings. Which would mean 150 apts total for the site and 6 service entrances.

                            I've always designed projects using 3Ø service feeders until this year. Per conversation with utility company 208 is cheaper than 480. And 1Ø is also cheaper than 3Ø. There is an independent Elec Engineering company that designs the 1Ø isolation or converters for projects like these in our area. I would have imagined the 1Ø would cause the gear and feeders to be upsized and ultimately negated any savings from the phase converters or phase isolation.

                            Comment


                              #15
                              What kind of hoops you have to jump through for fault currents? 2000 amps 120/208 three phase is 750kVA XF, over 56k Isc.
                              Using 10kA breakers there?

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